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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Parse "zoneinfo" time zone file.
// This is a fairly standard file format used on OS X, Linux, BSD, Sun, and others.
// See tzfile(5), http://en.wikipedia.org/wiki/Zoneinfo,
// and ftp://munnari.oz.au/pub/oldtz/
package time
import (
"io";
"once";
"os";
)
const (
headerSize = 4 + 16 + 4*7;
zoneDir = "/usr/share/zoneinfo/";
)
// Simple I/O interface to binary blob of data.
type data struct {
p []byte;
error bool;
}
func (d *data) read(n int) []byte {
if len(d.p) < n {
d.p = nil;
d.error = true;
return nil;
}
p := d.p[0:n];
d.p = d.p[n:len(d.p)];
return p;
}
func (d *data) big4() (n uint32, ok bool) {
p := d.read(4);
if len(p) < 4 {
d.error = true;
return 0, false;
}
return uint32(p[0])<<24 | uint32(p[1])<<16 | uint32(p[2])<<8 | uint32(p[3]), true;
}
func (d *data) byte() (n byte, ok bool) {
p := d.read(1);
if len(p) < 1 {
d.error = true;
return 0, false;
}
return p[0], true;
}
// Make a string by stopping at the first NUL
func byteString(p []byte) string {
for i := 0; i < len(p); i++ {
if p[i] == 0 {
return string(p[0:i]);
}
}
return string(p);
}
// Parsed representation
type zone struct {
utcoff int;
isdst bool;
name string;
}
type zonetime struct {
time int32; // transition time, in seconds since 1970 GMT
zone *zone; // the zone that goes into effect at that time
isstd, isutc bool; // ignored - no idea what these mean
}
func parseinfo(bytes []byte) (zt []zonetime, ok bool) {
d := data{bytes, false};
// 4-byte magic "TZif"
if magic := d.read(4); string(magic) != "TZif" {
return nil, false;
}
// 1-byte version, then 15 bytes of padding
var p []byte;
if p = d.read(16); len(p) != 16 || p[0] != 0 && p[0] != '2' {
return nil, false;
}
// six big-endian 32-bit integers:
// number of UTC/local indicators
// number of standard/wall indicators
// number of leap seconds
// number of transition times
// number of local time zones
// number of characters of time zone abbrev strings
const (
NUTCLocal = iota;
NStdWall;
NLeap;
NTime;
NZone;
NChar;
)
var n [6]int;
for i := 0; i < 6; i++ {
nn, ok := d.big4();
if !ok {
return nil, false;
}
n[i] = int(nn);
}
// Transition times.
txtimes := data{d.read(n[NTime]*4), false};
// Time zone indices for transition times.
txzones := d.read(n[NTime]);
// Zone info structures
zonedata := data{d.read(n[NZone]*6), false};
// Time zone abbreviations.
abbrev := d.read(n[NChar]);
// Leap-second time pairs
d.read(n[NLeap]*8);
// Whether tx times associated with local time types
// are specified as standard time or wall time.
isstd := d.read(n[NStdWall]);
// Whether tx times associated with local time types
// are specified as UTC or local time.
isutc := d.read(n[NUTCLocal]);
if d.error { // ran out of data
return nil, false;
}
// If version == 2, the entire file repeats, this time using
// 8-byte ints for txtimes and leap seconds.
// We won't need those until 2106.
// Now we can build up a useful data structure.
// First the zone information.
// utcoff[4] isdst[1] nameindex[1]
z := make([]zone, n[NZone]);
for i := 0; i < len(z); i++ {
var ok bool;
var n uint32;
if n, ok = zonedata.big4(); !ok {
return nil, false;
}
z[i].utcoff = int(n);
var b byte;
if b, ok = zonedata.byte(); !ok {
return nil, false;
}
z[i].isdst = b != 0;
if b, ok = zonedata.byte(); !ok || int(b) >= len(abbrev) {
return nil, false;
}
z[i].name = byteString(abbrev[b:len(abbrev)]);
}
// Now the transition time info.
zt = make([]zonetime, n[NTime]);
for i := 0; i < len(zt); i++ {
var ok bool;
var n uint32;
if n, ok = txtimes.big4(); !ok {
return nil, false;
}
zt[i].time = int32(n);
if int(txzones[i]) >= len(z) {
return nil, false;
}
zt[i].zone = &z[txzones[i]];
if i < len(isstd) {
zt[i].isstd = isstd[i] != 0;
}
if i < len(isutc) {
zt[i].isutc = isutc[i] != 0;
}
}
return zt, true;
}
func readinfofile(name string) ([]zonetime, bool) {
buf, err := io.ReadFile(name);
if err != nil {
return nil, false;
}
return parseinfo(buf);
}
var zones []zonetime
func setupZone() {
// consult $TZ to find the time zone to use.
// no $TZ means use the system default /etc/localtime.
// $TZ="" means use UTC.
// $TZ="foo" means use /usr/share/zoneinfo/foo.
tz, err := os.Getenverror("TZ");
switch {
case err == os.ENOENV:
zones, _ = readinfofile("/etc/localtime");
case len(tz) > 0:
zones, _ = readinfofile(zoneDir+tz);
case len(tz) == 0:
// do nothing: use UTC
}
}
func lookupTimezone(sec int64) (zone string, offset int) {
once.Do(setupZone);
if len(zones) == 0 {
return "UTC", 0;
}
// Binary search for entry with largest time <= sec
tz := zones;
for len(tz) > 1 {
m := len(tz)/2;
if sec < int64(tz[m].time) {
tz = tz[0:m];
} else {
tz = tz[m:len(tz)];
}
}
z := tz[0].zone;
return z.name, z.utcoff;
}
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